weird fixed-gear problems

Mike Baranczak said:

So I just finished building up my first fixie from a 70s Windsor frame
that was rescued from a dumpster. Everything seems cool, except the
chain doesn't seem to mesh with the sprocket properly. At the spot where
its coming onto the sprocket, it sometimes sits on top of the teeth
before it drops down, which gives it a really rough quality when I'm
pedaling. It almost looks like the chain links are slightly too short,
or like the teeth extend too far out.

Anybody seen anything like this before? The chain line is straight, as
far as I can tell, and it's not a question of too much tension, because
it still happens when there's slack in the chain. I have an old Sugino
crank in the front, a brand-new SRAM 1/8" single-speed chain, and a
brand-new Surly 1/8" sprocket with 14 teeth.

I assume that the problem is happening where the chain feeds onto the
front sprocket; the problem is typical of what can happen with badly
worn teeth. I'd say the old sprocket was shot when you rescued the
bike.
--
Typoes are a feature, not a bug.
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In article <[email hidden]>,

Werehatrack said:

Mike Baranczak said:

So I just finished building up my first fixie from a 70s Windsor frame
that was rescued from a dumpster. Everything seems cool, except the
chain doesn't seem to mesh with the sprocket properly. At the spot where
its coming onto the sprocket, it sometimes sits on top of the teeth
before it drops down, which gives it a really rough quality when I'm
pedaling. It almost looks like the chain links are slightly too short,
or like the teeth extend too far out.

Anybody seen anything like this before? The chain line is straight, as
far as I can tell, and it's not a question of too much tension, because
it still happens when there's slack in the chain. I have an old Sugino
crank in the front, a brand-new SRAM 1/8" single-speed chain, and a
brand-new Surly 1/8" sprocket with 14 teeth.

I assume that the problem is happening where the chain feeds onto the
front sprocket; the problem is typical of what can happen with badly
worn teeth. I'd say the old sprocket was shot when you rescued the
bike.

No no, the front chainring's looking fine. This is happening in the
rear, and like I said, all the parts back there are new.

-MB

Mike Baranczak said:

So I just finished building up my first fixie from a 70s Windsor frame
that was rescued from a dumpster. Everything seems cool, except the
chain doesn't seem to mesh with the sprocket properly. At the spot where
its coming onto the sprocket, it sometimes sits on top of the teeth
before it drops down, which gives it a really rough quality when I'm
pedaling. It almost looks like the chain links are slightly too short,
or like the teeth extend too far out.

Either the sprocket is badly worn, or you have chainline problems. Line
up the chainring with the rear sprocket by using a straightedge laid
along the face of the chainring. It should just contact the
corresponding face of the sprocket. If not, either re-position the
chainring (if it is on a double crank, swap sides), or put a spacer in
the hub to move the sprocket over. Either old bottom-bracket spacers, or
cassette spacers, will do.

Quoted message said:

Anybody seen anything like this before? The chain line is straight, as
far as I can tell,

How do you determine this?

--

David L. Johnson

__o | "A foolish consistency is the hobgoblin of little minds, adored
_`\(,_ | by little statesmen and philosophers and divines." --Ralph Waldo
(_)/ (_) | Emerson

In article <[email hidden]>,

David L. Johnson said:

Mike Baranczak said:

So I just finished building up my first fixie from a 70s Windsor frame
that was rescued from a dumpster. Everything seems cool, except the
chain doesn't seem to mesh with the sprocket properly. At the spot where
its coming onto the sprocket, it sometimes sits on top of the teeth
before it drops down, which gives it a really rough quality when I'm
pedaling. It almost looks like the chain links are slightly too short,
or like the teeth extend too far out.

Either the sprocket is badly worn, or you have chainline problems.

Sprocket's brand new, so that leaves the chainline. I thought it was
straight, but I wasn't particularly careful about measuring it, so I
guess it could be off a little. I'll check it tomorrow and respace the
chainring if I have to. What sort of tolerance am I aiming for here? 2
millimeters? 5? 10?

-MB

Mike Baranczak said:

So I just finished building up my first fixie from a 70s Windsor frame
that was rescued from a dumpster. Everything seems cool, except the
chain doesn't seem to mesh with the sprocket properly. At the spot where
its coming onto the sprocket, it sometimes sits on top of the teeth
before it drops down, which gives it a really rough quality when I'm
pedaling. It almost looks like the chain links are slightly too short,
or like the teeth extend too far out.

Anybody seen anything like this before? The chain line is straight, as
far as I can tell, and it's not a question of too much tension, because
it still happens when there's slack in the chain. I have an old Sugino
crank in the front, a brand-new SRAM 1/8" single-speed chain, and a
brand-new Surly 1/8" sprocket with 14 teeth.

http://www.sheldonbrown.com/chains.html

Yes, the chain and sprocket are new. ("Is it plugged in?" method):
Measure the chain, as in the link above, to eliminate it as a possible
problem. See the photos of mixed new/old chain/cog on the Sheldon page.

Per Mr. Johnson's post, use a straightedge as a gauge, or use the tool
you measured your chain with to find chainline from center. Sheldon has
a section on this, and so does John Dacey:

http://www.businesscycles.com/tr-refspec.htm#chainline

There's a button in the J. Dacey link that goes to Sheldon's chainline
section. Worth reading both, IMHO. You want a perfect chainline (said
the converted sinner).

And the culprit is? --D-y

Mike Baranczak said:

So I just finished building up my first fixie from a 70s Windsor frame
that was rescued from a dumpster. Everything seems cool, except the
chain doesn't seem to mesh with the sprocket properly. At the spot where
its coming onto the sprocket, it sometimes sits on top of the teeth
before it drops down, which gives it a really rough quality when I'm
pedaling. It almost looks like the chain links are slightly too short,
or like the teeth extend too far out.

Anybody seen anything like this before? The chain line is straight, as
far as I can tell, and it's not a question of too much tension, because
it still happens when there's slack in the chain. I have an old Sugino
crank in the front, a brand-new SRAM 1/8" single-speed chain, and a
brand-new Surly 1/8" sprocket with 14 teeth.

http://www.businesscycles.com/tr-refspec.htm#chainline

There's a button in the J. Dacey page that goes to Sheldon Brown's
chainline section. Worth reading both, IMHO. You want a perfect
chainline (said the converted sinner), with chainring and cog both
being the same distance away from the frame's centerline.

Dumpster salvage? Might be a good idea to make sure this frame has a
centerline <g>! --D-y

Mike Baranczak said:

In article <[email hidden]>,

David L. Johnson said:

Mike Baranczak said:

So I just finished building up my first fixie from a 70s Windsor frame
that was rescued from a dumpster. Everything seems cool, except the
chain doesn't seem to mesh with the sprocket properly. At the spot where
its coming onto the sprocket, it sometimes sits on top of the teeth
before it drops down, which gives it a really rough quality when I'm
pedaling. It almost looks like the chain links are slightly too short,
or like the teeth extend too far out.

Either the sprocket is badly worn, or you have chainline problems.

Sprocket's brand new, so that leaves the chainline. I thought it was
straight, but I wasn't particularly careful about measuring it, so I
guess it could be off a little. I'll check it tomorrow and respace the
chainring if I have to. What sort of tolerance am I aiming for here? 2
millimeters? 5? 10?

-MB

I've never used the 1/8" stuff, perhaps it's more sensitive to chain
line. Are you sure the chain is really a 1/8" -- I don't know if a 3/16"
chain would even mesh with a 1/8" sprocket, but if it did it would
probably do as badly as you describe.

Ideally, I think you want to get your chain line within a couple of mm.

Peter Cole said:

I've never used the 1/8" stuff, perhaps it's more sensitive to chain
line. Are you sure the chain is really a 1/8" -- I don't know if a 3/16"
chain would even mesh with a 1/8" sprocket, but if it did it would
probably do as badly as you describe.

You don't mean 3/16", you mean 3/32". 3/16" was the width of old block
chain, with 1" pitch. Anyway, yes, 1/8" and 3/32" stuff works fine
together --- that is, you can use 1/8" chain with 3/32" sprockets and
chainrings. I currently have a 3/32" chainring, but 1/8" sprocket, so a
1/8" chain. 1/8" chain is probably more sensitive to a bad chainline, but
at least it is not designed to come off of the sprocket, like derailleur
chain is.

Quoted message said:

Ideally, I think you want to get your chain line within a couple of mm.

Indeed. 5mm is too far.

--

David L. Johnson

__o | If all economists were laid end to end, they would not reach a
_`\(,_ | conclusion. -- George Bernard Shaw
(_)/ (_) |

David L. Johnson said:

Peter Cole said:

I've never used the 1/8" stuff, perhaps it's more sensitive to chain
line. Are you sure the chain is really a 1/8" -- I don't know if a 3/16"
chain would even mesh with a 1/8" sprocket, but if it did it would
probably do as badly as you describe.

You don't mean 3/16", you mean 3/32". 3/16" was the width of old block
chain, with 1" pitch. Anyway, yes, 1/8" and 3/32" stuff works fine
together --- that is, you can use 1/8" chain with 3/32" sprockets and
chainrings.

Sorry, brain fart. I did mean 3/32" (standard chain). I was thinking
perhaps that the OP accidentally mixed a 3/32" chain with a 1/8"
sprocket, which might explain his symptoms -- or maybe not, I've never
tried it so I don't know if it would engage at all.

Peter Cole said:

Sorry, brain fart. I did mean 3/32" (standard chain). I was thinking
perhaps that the OP accidentally mixed a 3/32" chain with a 1/8"
sprocket, which might explain his symptoms -- or maybe not, I've never
tried it so I don't know if it would engage at all.

Oh, I didn't get that that was what you were saying. But a 3/32" chain
would never engage a 1/8" sprocket at all, so I doubt that that is it.

--

David L. Johnson

__o | Deserves death! I daresay he does. Many that live deserve
_`\(,_ | death. And some that die deserve life. Can you give it to
(_)/ (_) | them? Then do not be too eager to deal out death in judgement.
-- J. R. R. Tolkein

Peter Cole said:

David L. Johnson said:

Peter Cole said:

I've never used the 1/8" stuff, perhaps it's more sensitive to chain
line. Are you sure the chain is really a 1/8" -- I don't know if a
3/16" chain would even mesh with a 1/8" sprocket, but if it did it
would probably do as badly as you describe.

You don't mean 3/16", you mean 3/32". 3/16" was the width of old
block chain, with 1" pitch. Anyway, yes, 1/8" and 3/32" stuff works
fine together --- that is, you can use 1/8" chain with 3/32"
sprockets and chainrings.

Sorry, brain fart. I did mean 3/32" (standard chain). I was thinking
perhaps that the OP accidentally mixed a 3/32" chain with a 1/8"
sprocket, which might explain his symptoms -- or maybe not, I've never
tried it so I don't know if it would engage at all.

It does, typically, but simply by the wedging force... the side plates
probably pop off pretty quickly.
--
Phil Lee, Squid

David L. Johnson said:

Peter Cole said:

Sorry, brain fart. I did mean 3/32" (standard chain). I was thinking
perhaps that the OP accidentally mixed a 3/32" chain with a 1/8"
sprocket, which might explain his symptoms -- or maybe not, I've never
tried it so I don't know if it would engage at all.

Oh, I didn't get that that was what you were saying. But a 3/32" chain
would never engage a 1/8" sprocket at all, so I doubt that that is it.

I've used my chain whip with 3/32" chain to spin 1/8" fixed cogs on and
off a wheel. The chain will engage the sprocket for a few teeth, but it
won't wrap around half of a 20 or 22 tooth cog. In fact, it acts much
like the OP described: some engagement, then it rides on the top of the
teeth.

I, too, would check the chain to be sure it's 1/8". Maybe the LBS can
test your sprocket with a piece of 1/8" chain. If their chain fits but
yours doesn't, you've found the culprit.

--
Dave
dvt at psu dot edu

Everyone confesses that exertion which brings out all the powers of body
and mind is the best thing for us; but most people do all they can to
get rid of it, and as a general rule nobody does much more than
circumstances drive them to do. -Harriet Beecher Stowe, abolitionist and
novelist (1811-1896)